A method of said type is known from US 2006/0219299 A1. In the case of the known method the actuating element or, as the case may be, the control valve is moved in the course of a partial-stroke test by means of the position controller from the respective current position over a part of its displacement path and is then moved back again. The change in position is so small in this case that the online operation of the plant in which the control valve is installed does not have to be interrupted and is disrupted only to an insignificant extent. During the partial-stroke test the displacement movement is recorded and stored.
In order to test the magnetic valve the latter is briefly deactivated through interruption of its voltage supply and in the process the pressure difference between the side of the magnetic valve connected to the position controller and the side connected to the actuating drive is monitored. The test of the magnetic valve is rated as successful if the pressure on the actuating drive side drops significantly during the temporary deactivation of the magnetic valve while the pressure delivered by the position controller remains largely unchanged.